The invention concerns a system that employs air to cool heat-accessible metallurgical vessels that are provided with separate annular supports.
Large-scale converters for producing steel and other heat-accessible metallurgical vessels, crucibles for example, are generally secured in an annular support separated by a gap of 100 mm or more.
Metallurgical vessels of this type can expand freely as the temperature increases. Still they are often so exposed to high tension and heat that they exceed their limits of expansion, resulting in permanent deformation of the vessel. Gradually and over the course of several years the vessel will expand to the extent that its surface comes into contact with the support, forces its way into it, or deforms it. Cracks may also occur in the surface of the vessel. The reason for this damage is that the pressure exerted by the vessel's fire-proof lining increases with temperature. Since the lining is considerably hotter than the surface of the vessel, the former tends to expand more powerfully than the vessel, even when the coefficient of expansion of the lining is approximately the same as that of the steel surface. Furthermore, as the lining wears down and becomes thinner, the temperatures of the surface will increase and the vessel will become weaker. These drawbacks are particularly severe in large vessels, the walls of which, because they are welded, cannot be as thick as desired.
Other problems can occur in situations for example when tiles with a high content of carbon are employed to prolong the life of the fireproof lining. Such tiles conduct heat especially well and can accordingly raise the temperature of the vessel's wall above the threshold of strength.
Whenever there is a risk of the pressure exerted by the lining and of the temperature of the vessel's surface exceeding permissible levels, the metallurgical vessel must be additionally cooled.
Cooling the conical converter hat at the top with water is known. Installing a water-employing cooling system in the gap between the wall of the vessel and the annular support is undesirable in practice, however, because it would make access to that area too difficult.
The vicinity of the annular support is accordingly preferably cooled with air. Known for example is an air-employing cooling system with what is called a pipe curtain inserted between the annular support and the vessel and blowing air radially onto the surface of the vessel through several evenly distributed individual nozzles.
This system has drawbacks that can be ascribed to the necessity of increasing the air pressure to attain adequate cooling. The nozzles occupy too much space between the annular support and the vessel. Furthermore, there is usually not enough space in an existing converter plant to install such a cooling system. Finally, the existing natural convection would be severely inhibited or even eliminated by the installation of such a system.
Another air-employing cooling system has an annular line below the annular support with nozzles aimed in from the side or up that inject air to augment the natural convection current. The drawback to this system, however, is that the cross-sections of the pipeline must be small enough for the pipe to fit in, meaning that the air absolutely must be compressed, and effective heat diversion requires too much compressed air. Furthermore, the comparatively small cross-sections of the piping employed in this system mean that it must make do with small volumes of air, resulting in only minimal cooling.
Also known, finally, is the uniform distribution of several steel rings along the circumference of a steel-mill converter to create, in conjunction with steel straps or strips of sheet metal, box-shaped channels to conduct the injected air.